1. Field of the Invention
The present invention relates to electronic signal filter technology and more particularly, to a cavity filter, which has feedback channels defined therein to enhance signal transmission and wave-absorbing components to remove surge waves from feedback frequency components, improving signal quality and enhancing signal transmission performance.
2. Description of the Related Art
Following fast development of communication technology, many advanced wired and wireless signal transmitting and receiving equipment have been created and are widely used in different fields. However, due to limited wireless communication channels, full bandwidth utilization is quite important. For full bandwidth utilization, communication capacity and quality must be well improved. As different frequency channels may be close to one another, channel isolation must be well done to prevent interference and to maintain signal transmission quality. However, it is not easy to remove noises effectively and achieve excellent channel-to-channel isolation.
A regular bandpass cavity filter (or diplexer) allows bi-directional communication of the energy at a particular frequency range over a single channel and attenuates the energy that is out of this particular frequency range. However, a cavity filter cannot completely isolate the stop-band energy, causing instability of a transmission signal at the stop-band frequency. A signal feedback design may be employed to regulate the energy at the stop-band frequency. FIGS. 5 and 6 illustrate a cavity filter (diplexer) according to the prior art. According to this design, the cavity filter (diplexer) A comprises a base member A1 defining therein a resonant chamber A0, an antenna port A2 disposed at the center of the resonant chamber A0, and two signal input/output ports A3 respectively disposed at the two distal ends of the resonant chamber A0. During operation of the cavity filter (diplexer) A, in case two feedback channels A4 are disposed in the base member A1 at two opposite lateral sides relative to the resonant chamber A0, signal feedback in the feedback channels A4 may cause surge waves B to interfere with the signal transmitting/receiving frequency, affecting signal stability.